Rotary potentiometers



Oct. 31, 1961 A. w. FRASER ET AI. 3,007,126

ROTARY POTENTIOMETERS Filed Jan. 13, 1959 2 Sheets-Sheet 1 @55 M LOO/V1.Jk

Oct. 31, 1961 A. w. FRASER ET AL 3,007,126

ROTARY POTENTIOMETERS Filed Jan. 13, 1959 2 Sheets-Sheet 2 A32 5 Fl 6. 9INVENTORS United States Patent 3,007,126 RQTARY POTENTIQMETERS Alton W.Fraser, Van Nuys, Joseph M. Looney, Jr., Tarzana, and Robert M. Martin,Van Nuys, Caliii, assignors to Technology Instrument Corporation ofActon,

a corporation of Massachusetts Filed Jan. 13, 1959, Ser. No. 786,480 14Claims. (Cl. 338172) This invention relates to rotary potentiometers andmore particularly to (1) improved stop means for limiting rotation ofthe slider element and (2) means operated by the stop means foractuating switches associated with the potentiometer.

The growing emphasis on miniaturization resulting from the need toreduce the bulk and weight of airborne electronic equipment hasnecessitated the development of small precision potentiometers that arecapable of withstanding sudden shock, have fine resolution, will notfail or become unreliable under continuous use, and can be linked withother electrical or electronic components to form a small compactpackage.

Unfortunately, the more compact a rotary potentiorneter, the moretroublesome it becomes to achieve a construction that permits fullresolution without sacrifice of strength, accuracy, or range of output.For the purposes of this specification, full resolution occurs when theslider is capable of scanning the resistance element from one end to theother. Since the output range is proportional to the length of theresistance element, it is desirable to employ as long a resistance aspossible. In a rotary potentiometer, this necessitates having theresistance element encompass almost a full circle. Theoretically, ofcourse, the angle covered by the resistance element may be as much as359 59' 59", the sole requirement being that the resistance stop shortof a full circle. In practice, it is very difiicult to achieve fullresolution of resistances exceeding 340 in precision otentiometers ofrelatively small size as, for example, a potentiometer contained in acylindrical case whose outside diameter is less than one inch. This isdue to the difiiculty in providing stops which will allow the slider orcontact arm to fully scan the resistance and still prevent it from covering a full 360. The stops must be sturdy enough to prevent the sliderfrom exceeding the limits of the resistance; but sturdy stops ofnecessity are of appreciable size. Heretofore, in otentiometers smallerthan one inch in diameter, stops of desired strength have been so largeas to limit rotation of the slider arm by as much as 20 degrees.

Accordingly, one of the primary objects of this invention is to providea rotary potentiometer having novel stop mechanism which permits thecontact arm to rotate through an angle up to approximately 359 (orgreater if desired, as in the case of a 360 winding with taps at O, 90,180, and 270 such as is used in a phase shifter) but which also issufiiciently sturdy to last for the life of the potentiometer.

In practice, it is often necessary to combine a potentiometer and twosnap-action switches in such a way that one switch is operated when thecontact arm reaches one end of its operating stroke and the other switchis operated when the contact arm reaches the other end of its operatingstroke. This is advantageous where it is desired to automaticallyreverse connections to an electrical or electronic component each timethe contact arm reaches one end of its stroke. Heretofore, it has beendifiicult to combine the potentiometer and two switches as a singlepackage without sacrificing precision control, range, or compactness.Accordingly, another object of the present invention is to combine arotary potentiometer employing novel stop mechanism and two snapactionswitches in such a manner that the snap-action switches are supportedand operated by the potentiometer.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a first form of potentiometer embodyingthe present invention;

FIG. 2 is a vertical or longitudinal section of the potentiometer ofFIG. 1;

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2;

FIG. 3a is an enlargement of a portion of FIG. 3;

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 2;

FIG. 5 is a perspective view of a second form of potentiometer embodyingthe present invention;

FIG. 6 is a vertical or longitudinal section of the potentiometer ofFIG. 5;

FIG. 7 is a plan view of the same potentiometer;

FIG. 8 is a plan view of the same potentiometer with the switches andswitch-actuating member removed; and

FIG. 9 is a plan view of the slider assembly.

Referring now to FIGS. 1-5, the first form of the invention comprisesthree cylindrical casing sections 2, 4, and 6 provided at their adjacentends with peripheral grooves 8 which function as seats for split rings10'. The latter, when tightened by screws 12, function to clamp thesections together as a unit. The topmost section 2 has an end wall 14provided at its center with a tapped opening in which is screwed abearing sleeve 16. Sleeve 16 surrounds and rotatably supports a shaft18. Shaft 18 extends through a top end wall 20' formed in casing section4, and its bottom end is journaled in a bearing sleeve 22 secured in abottom end wall 24 formed in casing section 6.

Secured to the bottom end of bearing sleeve 16 by means of anon-conductive ring 26 is an annular conductive ring 28. Attached toshaft 18 is a rotor 30* of the split-ring type. A screw 32 functions tofrictionally secure the rotor to the shaft. Rotor 30 has a curved spn'ngmember 34 provided at each end with rounded contact head 36 which rideson conductive ring 28. Also attached to rotor 30 is a leaf springcontact member 40 which slidably engages a resistance element 42 that isattached to the inside surface of easing section 2. The ends 44 and 46of resistance element 42 are secured by wire leads (not shown) to theterminals 48 and 50 respectively of a terminal block 52 attached to theoutside of easing section 2. The third terminal 54 of the same block isattached by a wire lead 56 to conductive ring 28. Rotor 39 functions toprevent upward relative movement of shaft 18. A split-retaining ring 58attached to shaft 18 and seated in the upper end of bearing sleeve 16prevents relative axial movement of the shaft in a downward direction.

Also mounted on shaft 13 but in rotatable relation thereto is arotatable stop member 61 having a short radial extension 62 which isbent to form 21 depending extension 64. Stop member 69 is held inslidable engagement with the top Wall 20 of casing section 4 by means ofa rotor 66. Rotor as is of the split-ring type and is held tightly onshaft 13 by means of screw 68. Rotor 66 has a frusto-conical extension70. Cooperating with stop member 69 are two spaced depending stop pins74 and 76 screwed to the to; end wall 20 of easing section 4. Pins 74and 76 are long enough to be engaged by radial extension 62 of themovable stop member 60 but not so long as to int rfere with extension 76of rotor 66. It is to be noted that the radial extension 62 is locatedbetween pins 74 and 76 and can be moved through an arcuate path equal inlength to the are between said pins less the are occupied by the widthof said extension 62.

Mounted in opposed slots in the side wall of casing section 6 are twosnap-action switches A and B. These switches are of the type havingspring-biased actuating buttons, the buttons 80 and 82 of switches A andB respectively being shown in dotted lines in PEG. 3a. As illustrated,switches A and B have three terminals. One terminal 84 is the commonterminal. The second terminal 36 is the normally open terminal. Thethird terminal 88 is the normally closed terminal.

Finger 64 extends down into casing section 6 far enough to be engageablewith switch buttons 36 and 32. As seen in FIG. 3a, the buttons 80 and 82are spaced from each other by an angle slightly less than the anglebetween stop pins 74 and 76. Thus, finger 64 will engage button 86 ofswitch A just before it engages stop pin 74 and will engage button 82 ofswitch 8 just before it engages stop pin 76.

Rotors 3i and 66 and resistance element 42 are so oriented that whenfinger 64 engages button 80, slider 46 will be at the end 44 ofresistance element 42; and when finger 64- engages button 82, slider towill be at the opposite end 46 of the resistance element. Assuming thenthat switches A and B are reversing switches connected to externalcircuitry to which is applied the output signal picked off by slider 36,switch A will be actuated when the signal is smallest-pr vice versa,depending on how the input signal is applied to resistance element Thestop elements automatically determine the length of the operating strokeof slider 46.

Assuming that stop member 60 is in the position shown in FIG. 3, rotor66 can be rotated clockwise but not counterclockwise. When rotor 66 isrotated clockwise, its extension 70 will pass first under pin 76 andthen under pin 74. As it passes under pin 74, it will engage finger andcause stop member 60 to rotate in the same direction until it is stoppedby pin 76. This in turn stops rotor 66 but leaves it free to rotatecounterclockwise to engage and drive stop element 60 back to itsoriginal position. In eflect, stop element 60 provides a limited amountof lost motion, enabling shaft 18 to be rotated through an angle nototherwise permissible except by the use of relatively small and,therefore, relatively weak stop elements. Yet, the illustratedconstruction is quite sturdy and dependable. Moreover, should it bedesired to increase the size of pins 74 and 76, the same angle ofmovement for rotors 66 and 30 can be achieved by placing the pinsfurther apart.

The second form of the invention is shown in FIGS. -9 and comprises acasing or housing 1%. Casing 1'56 has a bottom end wall 162 providedwith a. central opening 194 and a sleeve 106 formed coaxially with saidopening. Secured in opening 164 and sleeve 1436 is a pair of ballbearing members, each consisting of an outer race 163 and an inner race116. A shaft 112 extends through and is secured to the inner races 11%.

Frictionally seated on the upper end of sleeve 1% is a cap 114 formed ofinsulating material. The upper surface 116 of cap 114 is flat andembedded therein are three arcuate conductive strips 118, 120, and 122.Extending in the cap from its bottom end and secured to these conductivestrips are wire leads 124, 126, and 128. Theseleads extend through acommon opening in the casing and are connected to separate ones of theterminals 130 of a terminal board 132 which is attached to the outerside of the casing.

Secured to the inner surface of casing 100 are three separate wire-woundresistance elements 134, 136, and 138. Leads 140 and 142 are attached tothe opposite ends of resistor 134 leads 144 and 146 are attached to theopposite ends of resistor 136; and leads 148 and 150 are attached to theopposite ends of resistor 136. These leads also pass through the wall ofcasing 166" and are also attached to separate terminals 13%).

Attached to shaft 112 in spaced relation to cap 114 is a circular disk156 constructed of non-conductive material. Secured to the underside or"disk 156 by means of rivets 158 are three equiangulariy spacedconductive contact members 16%, 162, and 164. Tl'iese contact membersare constructed of resilient material and include downwardly inclinedportions 166 provided with hemispherical contacts 168 that engage theconductive strips on cap 114. The contacts 163 of members 16-0, 162, and16% contact conductive strips 113, 121 122 respectively. Also attachedto each contact member is a pair of spring wire sliders 17%. Sliders 173extend tangentially of disk 156 and are bent at their free ends to formrounded portions 172 that lightly engage the resistance elements.Sliders 17% of members 166, 162, and i6 3 slidably contact resistanceelements 134, 136, and respectively.

Shaft 112 also carries a radially extending pin 174 which is spacedvertically from disk 156. Pin 174- cooperates with a movable stop memberwhich extends across the casing. Stop member 176 has a relatively largecentral opening 177 through which extends shaft 112. One end 178 of stopmember 176 is pivotally secured by a screw 13% to a flat end surface 182formed by a cavity in the top end edge of the casing. The opposite endof stop member 176 is located in a second cavity also formed in the topend edge 186. Cavity 1556 defines a flat surface 191 on which rests thefree end 183 of the stop member. Cavities 18 and are diametricallyoppcsed. Casing 166 also has two tapped cores 192- and iint which areaxially aligned along a chord of the circle defined by the casing. Setscrews 196 and 198 are crewed into these holes. The free end 188 of stopmember 176 extends between set screws 1% and 198. The spacing betweenthese set screws determines the angular distance through which stopmember 176 may be pivoted. This spacing may be varied by advancing orretracting the screws. However, stop member 176 cannot be pivotedbeyond. the limits determined by the difference in diameter of shaft 112and central opening 177.

Stop member 176 has depending flanges 2% and 292 at its opposite edges.These edges depend far enough to be engaged by pin 1'74 when shaft 112is rotated. Engagement of pin 174 with these flanges causes pivotalmovement of the stop member, the latter pivoting to the extent permittedby set screws 1% and 198.

Casing also has two diametrically opposed slots 206 and 208 formed inits top end. These slots accommodate snap-action switches A and B.Tapped holes 210 are provided for screws 212 which function to securethe switches to the casing. Switches A and B are like the switches shownin the embodiment of FIGS. 1-4, having spring-biased actuating buttons214 and 216 respectively. Switch A is actuated when button 214 isengaged by flange 290 and switch B is actuated when button 216 isengaged by flange 202.

The several elements are oriented so that switch A is actuated whensliders 1'70 approach the ends of the resistance elements to which areattached leads 140, 144, and 143. Switch B is actuated when slidersapproach the opposite ends of the resistance elements to which areattached leads 142, 146, and 150. In practice, set screws 196 and 193may be set to prevent flanges 200 and 262 from actuating the switches ormay be set to stop movement of stop member 176 just as or just after theflanges contact switch buttons 214 and 216. Set screws 196 and 198 actto limit the operating stroke of sliders 170 by limiting the distancethrough which stop member 176 may be pivoted. Thus, set screws 196 and198 determine the maximum and minimum values of the voltages picked offby sliders 170.

It is believed to be apparent that by placing bores 192 and 194 in adifferent position and by changing the length of pin 174, it is possibleto increase the angle through which the stop member 176 may be pivoted.Similarly, the switches A and B may be omitted without disturbing thefunction of limiting the stroke of shaft 112 and sliders 120 which isperformed by the cooperative association of pin 174, stop member 176,and set screws 196 and 198.

Obviously, many modifications and variations of the present inventionare possible in the light of the above teachings. Therefore, it is to beunderstood that the in vention is not limited in its application to thedetails of construction and arrangement of parts specifically describedor illustrated, and that within the scope of the appended claims, it maybe practiced otherwise than as specifically described or illustrated.

I claim:

1. In a rotary potentiometer comprising a rotatable shaft, a resistanceelement arranged in concentric spaced relation to said shaft, a contactelement slidably engaging said resistance element, and means connectingsaid shaft and contact element whereby said contact element will rotatewith said shaft, a movable member movably mounted in a plane extendingtransversely of said shaft, a radially extending arm attached to saidshaft, first means on said movable member positioned to be engaged bysaid arm when said arm is rotated clockwise, whereby said movable memberwill be moved in a first direction by said arm, second means on saidmovable member poistioned to be engaged by said arm when said arm isrotated a predetermined amount counterclockwise away from said firstmeans, whereby said movable means will be moved in a second direction bysaid arm, third means limiting movement of said movable member in saidfirst direction, and fourth means limiting movement of said movablemember in said second direction.

2. The combination of claim 1 wherein said movable member is mounted forrotational movement.

3. The combination of claim 1 wherein said movable member is rotatablyconnected to said shaft.

4. The combination of claim 1 wherein said third and fourth means areadjustable to vary the extent of movement of said movable member.

5. The combination of claim 1 further including first and secondswitches, means supporting said first switch in position to be engagedand operated by said movable member as it moves in said first direction,and means supporting said second switch in position to be engaged andoperated by said movable member as it moves in said second direction.

6. The combination of claim 1 further including a casing surrounding andsupporting said resistance element, a bearing member attached to saidcasing and supporting said shaft, and first and second switches carriedby said casing, said first switch having an actuating member positionedto be engaged and operated by said movable member as said movable membermoves in said first direction, said second switch having an actuatingmember positioned to be engaged and operated by said movable member asit moves in said second direction.

7. In a rotary potentiometer comprising a circularly arranged resistanceelement, a casing surrounding and supporting said resistance element, ashaft, means rotatably supporting said shaft in said casing, anelectrical contact member slidably engaging said resistance element, andmeans for moving said contact member along said resistance element assaid shaft is rotated, the improvement comprising an arm on said shaft,a stop element pivotally connected to said casing, said stop elementextending across the interior of said casing in a position to be engagedand pivoted by said arm as said shaft is rotated, first stop means forlimiting pivotal movement of said stop element in a first direction, andsecond stop means spaced from said first stop means for limiting pivotalmovement of said stop element in a second direction opposite to saidfirst direction.

8. In a rotary potentiometer comprising a circularly arranged resistanceelement, a casing surrounding and supporting said resistance element, ashaft, means rotatably supporting said shaft in said casing, anelectrical contact member slidably engaging said resistance element, andmeans for moving said contact member along said resistance element assaid shaft is rotated, the improvement comprising an arm on said shaft,a stop element rotatably mounted on said shaft, said stop element comprising a disk having a depending finger positioned to be engaged andmoved by said arm as said shaft is rotated, and first and second fixedstop means spaced from each other and disposed so as to be engageabledirectly only by said finger when said shaft is rotated.

9. In a rotary potentiometer comprising a circularly arranged resistanceelement, a casing surrounding and supporting said resistance element, ashaft, means rotatably supporting said shaft in said casing, anelectrical contact member slidably engaging said resistance element, andmeans for moving said contact member along said resistance element assaid shaft is rotated, the improvement comprising an arm on said shaft,a stop element having one end pivotally connected to said casing, saidstop element extending laterally across the interior of said casing in aposition to be engaged and pivoted by said arm as said shaft is rotated,first stop means attached to said casing in position to be engaged byand block the opposite end of said stop element on pivotal movement ofsaid stop element in a first direction, and second stop means attachedto said casing in position to be engaged by and block said opposite endof said stop'element on pivotal movement of said stop element in asecond direction opposite to said first direction.

10. In a rotary potentiometer comprising a circularly arrangedresistance element, a casing surrounding and supporting said resistanceelement, a shaft, means rotatably supporting said shaft in said casing,an electrical contact member slidably engaging said resist-ance element,and means for moving said contact member along said resistance elementas said shaft is rotated, the improvement comprising an arm on saidshaft, a stop element having one end pivotally connected to said casing,said stop element extending laterally across the interior of said casingin a position to be engaged and pivoted by said arm as said shaft isrotated, first stop means attached to said casing for limiting pivotalmovement of said stop element in a first direction, and second stopmeans attached to said casing and spaced from said first stop means forlimiting pivotal movement of said stop element in a second directionopposite to said first direction, said first and second stop means beingset screws which are accessible externally of said casing and aremovable toward and away from each other whereby to adjust the spacingtherebetween.

11. In a rotary potentiometer comprising a circularly arrangedresistance element, a casing surrounding and supporting said resistanceelement, a shaft, means rotatably supporting said shaft in said casing,an electrical contact member slidably engaging said resistance element,and means for moving said contact member along said resistance elementas said shaft is rotated, the improvement comprising an arm on saidshaft, a stop element pivotally connected to said casing, said stopelement extending across the interior of said casing in a position to beengaged and pivoted by said armas said shaft is rotated, first stopmeans for limiting pivotal movement of said stop element in a firstdirection, second stop means spaced from said first stop means forlimiting pivotal movement of said stop element in a second directionopposite to said first direction, two switches attached to said casing,first means on said stop element for actuating one switch when said stopelement is pivoted in said first direction, and second means on saidstop element for actuating the other switch when said stop element ispivoted in said second direction.

12. In a rotary potentiometer comprising a circularly arrangedresistance element, a casing surrounding and supporting said resistanceelement, a shaft, means rotatably supporting said shaft in said casing,an electrical contact member slida-bly engaging said resistance element,and means for moving said contact member along said resistance elementas said shaft is rotated, the improvement comprising an arm on saidshaft, a stop element pivotally connected to said casing, said stopelement contained Wholly Within said casing and extending across theinterior of said casing in a position to be engaged and pivoted by saidarm as said shaft is rotated, first stop means for limiting pivotalmovement of said stop element in a first direction, and second stopmeans spaced from said first stop means for limiting pivotal movement ofsaid stop element in a second direction opposite to said firstdirection, said stop element having an opening through which said shaftextends, said opening being suificiently large to permit said stopelement to be pivoted between the limits determined by said first andsecond stop means.

13. In a rotary potentiometer comprising a circularly arrangedresistance element, a casing surrounding and supporting said resistanceelement, a shaft, means rotatably supporting said shaft in said casing,an electrical contact member slidably engaging said resistance element,and means for moving said contact member along said resistance elementas said shaft is rotated, the improvement comprising an arm on saidshaft, a stop element rotatably mounted on said shaft between said armand an end wall of said casing, said stop element comprising a diskhaving a depending finger positioned to be engaged and moved by said armas said shaft is rotated, and first and second stop pins anchored insaid end wall, said stop pins spaced from each other and disposed so asto be engageable directly only by said finger when said shaft isrotated.

14. In a rotary potentiometer comprising a circularly arrangedresistance element, a casing surrounding and supporting said resistanceelement, a shaft, means rotatably supporting said shaft in said casing,an electrical contact member slidably engaging said resistance element,and means for moving said contact member along said resistance elementas said shaft is rotated, the improvement comprising an arm on saidshaft, a stop element rotatably mounted on said shaft, said stop elementcomprising a. disk having a depending finger positioned to be engagedand moved by said arm as said shaft is rotated, first and second fixedstop means spaced from each other and disposed so as to be engageab ledirectly only by said finger when said shaft is rotated, a pair ofswitches supported by said casing, one of said switches disposed so asto be actuated by said finger when said stop element is rotated in onedirection by said arm, and the other of said switches disposed so as tobe actuated by said finger when said stop element is rotated in theopposite direction by said arm.

References Cited in the file of this patent UNITED STATES PATENTS611,185 Richardson et al Sept. 20, 1898 1,376,841 Tirrill May 3, 19211,804,243 Bond May 5, 1931 1,909,664 Douglas May 16, 1933 2,177,482 HallOct. 24, 1939 2,616,013 Greenlee Oct. 28, 1952

